How to Heat Up a Wood-Fired Hot Tub and Maintain Optimal Temperature (37–38°C)?

Wood-fired hot tubs offer a relaxing and natural way to unwind, but they require a bit of skill and timing to heat properly. Unlike electric hot tubs, where the temperature is controlled with the push of a button, wood-fired tubs demand attention to detail. Here’s a step-by-step guide to help you heat your tub efficiently and keep the temperature steady at a comfortable 37–38°C.

1. Prepare the Tub and Stove

Before starting the fire, make sure your hot tub is filled with clean water. Never light the stove when the tub is empty, as this can damage the heater. Use a thermometer to check the starting water temperature. Most tubs begin around 10–15°C depending on the season.

Open the stove’s air vents fully to allow maximum airflow. Place dry kindling and small logs inside the firebox. Using dry, seasoned hardwood will give you a cleaner, hotter, and longer-lasting burn.

2. Build the Fire Gradually

Light the kindling and gradually add more wood as the fire catches. Once the fire is well-established, you can add larger logs. Monitor the burn closely during the first 30–60 minutes to ensure consistent heating. Stir the water with paddle or mix it with turning on bubble systems occasionally to distribute the heat evenly.

Depending on the starting temperature and size of the tub, it can take 1.5–3 hours to reach 37–38°C. Keep the lid on during heating to retain heat and prevent debris from falling into the water.

3. Monitor the Temperature Carefully

Once the water reaches around 35°C, begin reducing the fire intensity. Close the air vents partially to slow the burn and stop adding wood unless you need a final push. Use a floating wireless thermometer to monitor the temperature accurately.

It’s important to anticipate the residual heat from the firebox—if the fire is still strong at 37°C, the temperature may continue to rise beyond the ideal range. Plan ahead and begin dampening the fire slightly before reaching 38°C.

4. Maintaining the Temperature

To keep the water between 37–38°C during use, feed the fire with small amounts of wood at regular intervals. Avoid large logs or overloading the stove, which can cause the temperature to spike. Stir the water occasionally and leave the lid slightly ajar if it begins to overheat.

During extended use, you may need to add more wood every 30–60 minutes. Be patient and make small adjustments. Having a small supply of pre-cut wood nearby makes this process smoother.

5. Post-Use Tips

After bathing, let the fire burn out naturally or remove unburned wood from the stove. Stir the water to help lower the temperature if needed, especially in warmer weather. Keeping the tub covered when not in use helps retain heat and prevents evaporation and debris buildup.

With practice, you’ll develop a feel for your tub’s heating pattern and how different woods and weather conditions affect the process. Enjoy the ritual—it’s part of what makes the wood-fired hot tub experience so rewarding.